The present invention generally relates to color graphics computers and displays. More particularly, the invention is directed to methods, systems and programs for logically partitioning an RGB graphics system of gamma ramp architecture to provide independent storage of multiple shaded color images. The methods, systems and programs are particularly valuable in animation applications, where the use of hardware defined overlays is limited by count or diversity of color.
Personal computers and workstations have evolved from those which generated simple monochrome alphanumeric images on a video display, to those capable of two-dimensional color graphics, and most recently into systems capable of generating three-dimensional color graphics with limited animation. The computational and time burden associated with rendering a complex (non-wire frame) object in fully shaded color is a challenge for all but supercomputers, if animation is desired. The difficulty is attributable to the fact that animation, and in particularly multiple object animation, requires not only that the animated object be regenerated, but also that the background be recreated upon a translation of the animated object or objects. Consequently, the animation of a complex shaped object in the context of a complex background is a significant challenge.
Available technological approaches to providing real-time animation all have drawbacks. The creation and movement of images in wireframe representation lacks the realism of a shaded image. Flipbook animation techniques, whereby a series of images are created and stored in incremental motion states for subsequent playback at real-time rates, do not permit the user to interact with the moving image and affect it in a contemporaneous fashion.
Even in the absence of full, photorealistic color animation, it is particularly desirable to have a personal computer or workstation with resources which allow a user to interact with three-dimensional color images at rates approaching real time. This situation exists independent of classical animation, such as when a graphics workstation user repositions a complex color image in the context of a complex color background.
The conventional solution to creating and moving complex images situated over a complex background in real time and without regeneration involves the use of overlays. A classical overlay is a single color grid pattern, which if superimposed on a complex video screen image is removable without requiring that the complex image be regenerated. A discussion of overlays, and in particular overlays which relate to specific windows on a video display, appears in U.S. Pat. No. 5,469,541. A common deficiency of overlays, which makes them undesirable for animation, is the low number of bits per pixel. A representative premium quality workstation will have four overlays of single bit information per overlay. Consequently, such design provides one overlay image of 15 colors, while fully consuming all overlay resources, if the animation is accomplished through the overlays.
High resolution color graphics workstations tend to follow one of two design approaches in the storage of color data within the frame buffer. The first class is generally known as "color index frame buffer storage". The second is generally referred to as "gamma ramp frame buffer storage". The former, color index frame buffer storage, typically uses up to 12 bits per pixel to provide a maximum range of approximately four thousand different colors per pixel position. The other, gamma ramp frame buffer storage, has each pixel position represented by 24 bits, composed of 8 bit red, 8 bit green and 8 bit blue segments. The gamma ramp implementation provides in excess of 16 million different colors, and as such is believed to approach the limits of human visual color differentiation.
The problem of providing animation for complex shaped and colored images and backgrounds in real-time and in the context of a gamma ramp configured workstation has proven to be elusive. Neither the architectures of conventional overlays nor the look-up table implemented digital to analog converters (commonly identified as RAMDACs) have the overlay bit content or pin count resources to avail a conventional workstation user of meaningful animation capability.